• Journal of the Korean Ceramic Society
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• v.23 no.3
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• pp.1-8
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• 1986

The preparation and electrical conductivity of $\beta$-$Al_2O_3$ are investigated as a function of $Na_2O$ content from the-oretical composition of $\beta$-$Al_2O_3$ to that of $\beta$"-$Al_2O_3$. $\beta$-$Al_2O_3$ $\beta$"$Al_2O_3$$\alpha$-Al2O3 and ${\gamma}$-NaAlO2 phases appear in the calcined powder at 125$0^{\circ}C$ for 2 hours. The majoity phase is $\beta$-$Al_2O_3$ in sintered specimens at 155$0^{\circ}C$ and 1$650^{\circ}C$ for 30 mins respectively and ${\gamma}$-4NaAlO_2$ phase also exists when Na2O content is over 10.39w/o ${\gamma}$-4NaAlO_2$ phase does not affect the grain growth of $\beta$-$Al_2O_3$ in sintering at 155$0^{\circ}C$ but acts as a reactive liquid for the abnormal grain growth of $\beta$-$Al_2O_3$in sintering at 1$650^{\circ}C$ The electrical conduction of $\beta$-$Al_2O_3$is predominated by 4Na^+$ ion. Contribution of ionic con-ductivity to total conductivity is gradually decreased with increasing temperature at given oxygen pressure and to -tal conductivity is increased by positive hole due to interstitial oxygen with increasing oxygen pressure.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.5
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• pp.187-191
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• 2019

Perovskite-type oxides have consistently attracted considerable attention for their applications in high-temperature electrochemical devices, such as electrolytes and electrodes of solid oxide fuel cells, oxygen permeating membranes and sensors etc. Among them, the electrical conductivity of 10 % Sr and 10 % Mg doped $LaAlO_3$ (LSAM9191) was measured using impedance spectroscopy and 4-probe d.c. method. Below $550^{\circ}C$, the grain boundary resistance mostly determined the overall conductivity; however, it nearly disappeared above $800^{\circ}C$. Using the defect model and curve fitting, the ionic and electronic conductivity contributions were also separated. In the temperature region where the sample resistance is mostly determined by the grain volume property, LSAM9191 was an oxygen ion conductor at low $Po_2$ and a mixed conductor at high $Po_2$. With increasing temperature, the ionic conduction region only slightly increased. Thus, LSAM9191 is a promising material as an oxygen ion conductor at high temperature and in low $Po_2$.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.358-358
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• 2012

The application of BZO (Boron-doped Zinc Oxide) films use as the TCO(Transparent Conductive Oxide) material for display and solar cell industries, where the conductivity of the BZO films plays a critical role for improvement of cell performance. Thin BZO films are deposited on glass substrates by using RF sputter system. Then charging flow rates of O2 gas from zero to 10 sccm, thereby controlling the impurity concentration of BZO. BZO deposited on soda lime glass and RF power was 300 W, frequency was 13.56 MHz, and working pressure was $5.0{\times}10-6$ Torr. The Substrate and glass between distance 200 mm. We measured resistivity, conductivity, mobility by hall measurement system. Optical properties measured by photo voltaic device analysis system. We measured surface build according to oxygen flow rate from XPS (X-ray Photoelectron Spectroscopy) system. The profile of the energy distribution of the electrons emitted from BZO films by the Auger neutralization is measured and rescaled so that Auger self-convolution arises, revealing the detail structure of the valence band. It may be observed coefficient ${\gamma}$ of the secondary electron emission from BZO by using ${\gamma}$-FIB (Gamma-Focused Ion Beam) system. We observed the change in electrical conductivity by correlation of the valence band structure. Therefore one of the key issues in BZO films may be the valence band that detail structure dominates performance of solar cell devices. Demonstrating the secondary electron emission by the Auger neutralization of ions is useful for the determination of the characteristics of BZO films for solar cell and display developments.

• Journal of Korean Society of Forest Science
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• v.89 no.2
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• pp.241-248
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• 2000

This research was conducted to investigate the physicochemical characteristics of stream water at the four points in the northeastern part of Puk'ansan National Park from July, 1998 to November, 1999. The average pH of stream water was 6.65 and dissolved oxygen was $10.7mg/{\ell}$, which indicated that the quality could be categorized in the first class for the quality of river water quality standard. In addition, the water was soft water and average percentage of dissolved oxygen was 96.7%, which was almost saturated. The number of visitors resulted in the increase of dissolved ion, witch affected on electrical conductivity of the water. The relationships between those factors was significant at the 1% level in linear regression. The electrical conductivity and the amount of anion($Cl^-$, $NO{_3}^-$, $SO{_4}^{2-}$)in downstream were higher than those in upstream.

• Journal of Electrochemical Science and Technology
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• v.2 no.1
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• pp.45-50
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• 2011

A series of expanded graphites is prepared from graphite oxide by changing the heat-treatment temperature, and their lithiation/de-lithiation mechanism and rate performance are examined. A featureless sloping profile is observed in their charge-discharge voltage and dilatometry profiles, which is contrasted by the stepwise plateau-like profiles observed with the pristine graphite. With an increase in the heat-treatment temperature from $250^{\circ}C$ to $850^{\circ}C$, the interlayer distance becomes smaller whereas the electric conductivity becomes larger, both of which are resulted from a removal of foreign atoms (mainly oxygen) from the interlayer gaps. The expanded graphite that is prepared by a heat-treatment at $450^{\circ}C$ delivers the best rate performance, which seems to be a trade-off between the $Li^+$ ion diffusivity that is affected by the interlayer distance and electrical conductivity.

• Bulletin of the Korean Chemical Society
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• v.35 no.5
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• pp.1465-1468
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• 2014

In this study, an intermediate temperature ionic conductor, $Ce_{0.95}Eu_{0.05}P_2O_7$, was prepared by solid state reaction. The variation of conductivities with the pressure $pH_2O$ or time were studied. The highest conductivity of $Ce_{0.95}Eu_{0.05}P_2O_7$ sample was observed in dry air atmosphere at $300^{\circ}C$ to be $1.1{\times}10^{-4}S{\cdot}cm^{-1}$ and in wet air atmosphere ($pH_2O=7.4{\times}10^3Pa$) at $100^{\circ}C$ to be $1.4{\times}10^{-3}S{\cdot}cm^{-1}$, respectively. The log ${\sigma}$ ~ log ($pO_2$) plot result indicated that $Ce_{0.95}Eu_{0.05}P_2O_7$ was almost a pure ionic conductor under high oxygen partial pressure and a mixed conductor of ion and electron under low oxygen partial pressure.

• Journal of Surface Science and Engineering
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• v.39 no.6
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• pp.250-254
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• 2006

Effect of hydrogen partial pressure ratio on the structural and electrical properties of highly c-axis oriented ZnO films deposited by oxygen ion-assisted pulsed filtered vacuum arc at a room temperature was investigated. The hydrogen partial pressure ratio were $1.4%\sim9.8%$ at 40% oxygen pressure ratio. The conductivity of ZnO:H films was increased from 1.4% up to 4.2% due to relatively high carrier mobility caused by improvement of crystallinity While the conductivity of ZnO:H films were decreased over than 4.2% and (0002) orientation was also deteriorated. The lowest resistivity of ZnO:H films was $2.5{\times}10^{-3}\;{\Omega}{\cdot}cm$ at 4.2% of hydrogen pressure ratio. Transmittance of ZnO:H films in visible range was 85% which is lower than that of undoped ZnO films because of declined preferred orientation.

• Journal of the Korean Chemical Society
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• v.31 no.4
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• pp.301-307
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• 1987

The electrical conductivity of highly pure polycrystalline sample of $La_2O_3$ has been measured at temperatures from $600^{\circ}C$ to $1,050^{\circ}C$ and oxygen pressure range of $1{\times}10^{-6}$ torr to $1{\times}10^2$ torr. The defect structure and semiconductor type are investigated by measuring the temperature and oxygen pressure dependences of electrical conductivity. Sintered $La_2O_3$ exhibits the electrical conductivities in the range of $1{\times}10^{-9}\;to\;1{\times}10^{-3}\;ohm^{-1}{\cdot}cm^{-1}$ under the above oxygen pressures. The oxygen pressure dependences on electrical conductivity are characterized by 5.3 at $1,000^{\circ}C$ and 5.7 at $700^{\circ}C$ and more higher values of 9∼14 below $700^{\circ}C$. The increase in n value with decreasing temperature indicates that a simple conduction mechanism does not exist in this material. The conduction carriers are not metal vacancy but oxygen ion at lower pressures. The conduction data indicate a significant ionic conduction at lower temperatures and electronic conduction at higher temperatures.

• Bulletin of the Korean Chemical Society
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• v.15 no.8
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• pp.636-640
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• 1994

The nonstoichiometric perovskite solid solutions of the $Nd_{1-x}Sr_xFeO_{3-y}$ system for the compositions of x=0.00, 0.25, 0.50, 0.75, and 1.00 have been prepared at $1150^{\circ}C$ in the air pressure. The compound of x=0.00, NdFe$O_{3.0}$, contains only $Fe^{3+}$ ion in octahedral site and the others involves the mixed valence state between $Fe^{3+}$ and $Fe^{4+}$ ions. The mole ratio of $Fe^{4+}$ ion or the ${\tau}$-value increases steadily with the x-value and then is maximized at the compositionof x= 1.00. The nonstoichiometric chemical formulas of the system are formulated from the x, ${\tau}$ and y values. From the Mossbauer spectroscopy, the isomer shift of $Fe^{3+}$ ion decreases with the increasing x-value, which is induced by the electron transfer between the$Fe^{3+}$ and $Fe^{4+}$ ions. The transfer is made possible by the indirect interaction between $Fe^{3+}$ and$Fe^{4+}$ ions via the oxygen ion. The eg electrons of the$Fe^{3+}$ ions are delocalized over all the Fe ions. Due to the electron transfer, the activation energy of electrical conductivity is decrease with the increasing amount of $Fe^{4+}$ ion.

• Bulletin of the Korean Chemical Society
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• v.16 no.3
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• pp.261-264
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• 1995

A series of samples of the Nd1-x(Ba0.40Mg0.60)1+xFeO4-y (x=0.00, 0.10, 0.20, and 0.30) system has been synthesized at 1450 ℃ under an atmospheric air pressure. The x-ray powder diffraction analysis of the solid solutions assigns the structure of all the compositions to orthorhombic system. Mohr salt analysis shows that τ and y values increase with x value and nonstoichiometric chemical formulas of the system can be formulated from the x, τ, and y values. Oxygen vacancies are distributed along c-axis in the perovskite layer. The magnetic ordering temperature remains unchanged with x value. Electrical conductivity and activation energy depend only on the mixed valence state of Fe ion. Conduction mechanism can be suggested as the hopping of electron between eg orbitals of Fe3+ and Fe4+ ions through Fe3+-O-Fe4+ bonds. Magnetic susceptibility and electrical conductivity are discussed with the nonstoichiometric chemical formulas.